U.S. Pat. Nos. 5,324,335 and 5,504,118 disclose the production of roughly spherical iron-based Fischer-Tropsch catalyst particles having diameters in the range of between 1 and 50 microns which are annealed by heating in air at about 316° C. (600° F.) to drive off residual moisture and to stabilise the catalyst. The annealing step i.e. the heating and gradual controlled cooling, converts the Goethite to Hematite whereafter the catalyst may be activated and used. According to these patents, the annealing does not lead to a breakage resistant or a superior performance catalyst particle.
South African Patent No. 90/7530 discloses the production of an iron-based Fischer-Tropsch catalyst including from 1 to 80% by mass of activated carbon. This catalyst shows improved breakage resistance over conventional catalyst, particularly where the particle diameters are below about 45 micron. The catalyst particle of this patent does not have superior synthesis performance and is expected to hydrothermally sinter at about 300° C.
A need thus exists for breakage resistant iron-based Fischer-Tropsch catalyst particles, in particular for use in a low temperature Fischer-Tropsch process, such as that carried out in a slurry bed reactor, for the production of, amongst others, wax and other syncrudes, as well as chemicals. The breakage resistant self-supported precipitated iron-based Fischer-Tropsch catalyst particles will ideally inhibit the formation of catalyst fines in the reactor thereby maintaining the performance of the reactor and reduce the contamination of down stream processes and catalysts by the catalyst fines.
In this specification, unless the context clearly indicates to the contrary, the term “fines” when used in relation to catalysts and catalyst particles is to be understood to mean particles which due to their dimensions, when present at a concentration of about 30% of the total catalyst, tend to reduce the performance of the solid separation system of a Fischer-Tropsch slurry bed reactor. Typically fines have a diameter of less than about 45 microns, usually about 22 microns.
A further long felt need which exists is that for self-supported precipitated iron-based Fischer-Tropsch catalyst particles having superior synthesis performance or activity, in particular for use in a low temperature Fischer-Tropsch process, such as that carried out in a slurry bed reactor, for the production of wax and other syncrudes, as well as chemicals.